A swaging structure is conventionally often used to connect metallic members to each other. The swaging structure has a configuration in that, in a hole portion provided in one metallic member, a fitted portion of another metallic member is fitted, thereafter, a pawl portion provided on the fitted portion is deformed to be engaged with a circumference of the hole portion of the one metallic member. The swaging structure is often used for terminals of batteries, various connectors and so on.
As an example using the swaging structure, there is a connection plate (bus bar) to connect electrode terminals of a plurality of batteries. In recent years, the bus bar has been used for an assembled battery (batter module) installed on hybrid vehicles or electric vehicles in place of conventional gasoline vehicles, and the demand for the bus bar is increased. In such an in-vehicle use, a battery module in which a plurality of lithium-ion batteries which are secondary batteries are connected in series is used. In the battery module, a bus bar to electrically connect electrode terminals of the plurality of assembled lithium-ion batteries (battery cells) is used. The bus bar is formed as a rectangular metallic plate having a pair of electrode terminal-inserting holes to insert the electrode terminals therein (Patent Documents 1 and 2)
In addition, there is a case where the pair of electrode terminals are made of heterogeneous metallic materials. Therefore, the bus bar is often formed by fitting a conductive member made of a dissimilar metallic material to a metallic plate in the metallic plate. The conductive member has a terminal hole to insert one of the electrode terminals therein. For example, if the battery cell is a lithium-ion battery, a positive electrode is made of an aluminum material and a negative electrode is made of a copper material. In this case, the metallic plate is made of a copper material and the conductive member is made of an aluminum material which is similar to one of the electrode terminals.
The bus bar is bridged between the plurality of battery cells by inserting electrode terminals in the pair of electrode terminal-inserting holes the metallic plate and fastening the metallic plate to the electrode terminals by use of bolts and nuts and so on to electrically connect the metallic plate and the electrode terminals. In this way, because a large number of bus bars are used for the battery module depending on the number of a combination of battery calls, an electric resistance of the bus bars becomes high. In addition, as mentioned above, in the bus bars used in the lithium-ion battery employed in the hybrid vehicles or the electric vehicles, because the conductive member is combined to the metallic plate made of a dissimilar metallic material to that of the conductive member, it is not possible to ignore an electric resistance at a junction portion between the metallic plate and the conductive member, this fact makes an impact to electric conversion efficiency or durability.